As spring lingers into summer and the Sun's path across the sky lengthens and the days warm, the Yosemite Valley becomes one of the most enchanting places in the world.

Waterfalls that have ebbed, if not vanished during winter, return with frothing fury, drawing the eyes of hundreds of thousands gathered in the valley to witness the spectacle.

Those visitors cram themselves into the valley that is synonymous with the entire Yosemite National Park, squeezing their cars onto road shoulders (and sometimes meadow grasses), herding down to the Merced River to enjoy the cool waters, and sometimes even creating traffic jams that leave roughly 1,000 idling vehicles on the seven-mile-long valley's narrow roads.

"The one thing that pops up over and over (in visitor surveys) are those peak days when we have that crowding," Kathleen Morse, the park's chief of planning, said during a discussion of how her staff approached a management plan that could protect the Merced River from the visitors. "It really detracts from the experience, and we really need to work on that."

The park's work on resolving the crowding issue, and the crowds' impacts on the Yosemite Valley in general and the Merced River specifically, is contained within the roughly 2,500-page-long Merced River Plan. The draft document was released publicly on January 8 for several months of public review and comment.

Twice previously Yosemite officials released a draft management plan intended to provide protection for the "outstandingly remarkable values" of the Merced River, which was designated in 1987 as a "recreational" river through the Yosemite Valley under the Wild and Scenic Rivers Act. Both times the plan was struck down by the courts.

In the most recent rejection, by the 9th U.S. Circuit Court of Appeals in February 2008, the judges both directed the park staff to set a daily visitation capacity limit for the river corridor through the valley and quite clearly implied that the Park Service needed to consider reducing commercial activities that do not "protect or enhance" the Merced's unique values.

In approaching for the third time the task of preparing a viable plan for the valley, Ms. Morse and her staff spent a great deal of time surveying park visitors for what they wanted from a Yosemite Valley experience.

"They really wanted us to make sure that these experiences that they’ve had over time, the family connection, the camping opportunities, the kind of eclectic lodging accommodations, just the essence of Yosemite was really important to maintain," she said.

“They didn’t want to see a big shift in the heart of what the Yosemite experience is. They wanted those things to be kept over time, because they’ve shared them from generation to generation," Ms. Morse went on. "They also wanted to have the freedom of access to Yosemite by private vehicle, and have the ability to make the choice, if they came on public transit or not, they wanted to bring their cars as an option. They wanted traffic congestion and crowding to be reduced."

But they were clear that they wanted to continue to enjoy lazy floats down the Merced River through the valley's heart, to roast marshmallows over an open fire at night in Housekeeping Camp, to pitch tents in the valley where their parents and, perhaps, grandparents had in years gone past, to lay down in the valley's grassy meadows to warm themselves under the Sun while watching climbers on El Capitan. And they wanted their personal vehicles, as well as less congestion at the same time.

But not all of those past practices were impact-free. Shorelines along the Merced long have been trampled by crowds flocking to the water, some Housekeeping Camp units were in the river's flood zone, social trails took root across the meadows as visitors wandered here and there.

To meet both the public's desires, and to protect the "outstandingly remarkable values" of the Merced River, the Yosemite planning staff hired engineers to monitor traffic flows, weighed which commercial uses were reasonable and which were not, looked at flood zones, and studied how they might relocate development around the valley floor to bolster both recreation and environmental protection.

What they decided was that by relocating parking areas, by removing some Housekeeping Camp units, demolishing a bridge (the Sugar Pine Bridge), by adding boardwalks and fencing, taking out the Curry Ice Rink and even doing away with the horseback ride concession, by adding a 36-site RV campground, boosting campsite numbers to 690 over the current 565, and by adding 111 day-use parking spots for a total of 2,448, they could not only maintain visitation levels in the valley at current levels of just under 20,000 per day, but also restore 203 acres in the valley and improve traffic flows so visitors aren't idling on the roads.

"What people value is part of what the national parks are all about, getting people to experience the national parks, and Yosemite is such a magnificent place," Ms. Morse said in describing the public's desires for a management plan. "We wanted to do it justice with this plan and raise the bar, both in protecting resources and in providing a quality visitor expereince, and I think we’ve got a good balance in the preferred alternative."

Public comment is being taken on the plan through April 18.